Assembly lines for automobiles and automobile parts automatically install automobile parts using articulated robots (see, for example, Japanese Laid-Open Patent Publication No. 2000-210825). Japanese Laid-Open Patent Publication No. 2000-210825 discloses an installation apparatus for automatically installing tires, one of heavy parts, onto automobile bodies using articulated robots. More specifically, the installation apparatus disclosed in Japanese Laid-Open Patent Publication No. 2000-210825 includes a tire installing mechanism (32) for automatically installing a tire (20) on a vehicle, the tire installing mechanism (32) having a plurality of nut runners (114a through 114d, 116) for placing as many nuts (24) as the number of hub bolts onto the vehicle at given circumferential intervals, a nut supply mechanism (22) for supplying nuts (24), one at a time, in a vertical attitude, and a nut arranging mechanism (33) for placing the nuts (24) supplied from the nut supply mechanism (22) in a circular pattern at circumferential intervals at which all of the nut runners (114a through 114d, 116) are arranged in a circular pattern, and transferring the nuts (24) to the nut runners (114a through 114d, 116) (see abstract of Japanese Laid-Open Patent Publication No. 2000-210825).
Certain assembly lines for automobiles and automobile parts employ a balancer for helping the worker in moving heavy parts (see, for example, Japanese Laid-Open Patent Publication No. 2001-139300). The balancer disclosed in Japanese Laid-Open Patent Publication No. 2001-139300 produces an upward force depending on the weight of a load (2) when the load (2) is suspended on a hook (16). The worker can move the cargo (2) horizontally through an arm (1) by applying a horizontal external force. The worker can also move the cargo (2) vertically through the arm (1) by operating an operating lever (17) (see, for example, paragraphs [0006] through [0008] and FIG. 1 of Japanese Laid-Open Patent Publication No. 2001-139300).